The 24-year-old partnered the South Korean international in midfield against Trabzonspor at the weekend, and Ephraim was grateful for the opportunity to play alongside the former Manchester United player.
Ephraim told the club's official website: "Ji is a fantastic player. He is a class act, both on and off the pitch and it has been great to play in the centre with him.
"I've not really played there before. I have only played as part of a three-man midfield so I am learning things all the time and taking things on board as much as I can."
Ephraim made two appearances for Queens Park Rangers in the Premier League last season.